Twitter has begun automatically shortening URLs pasted into tweets by its users, the microblogging site announced today.

When users compose a tweet and paste a link of any length into the Tweet box, Twitter will automatically abbreviate the link to 19 characters when users hit send. In testing for almost exactly a year, the service--called t.co--is being rolled out incrementally and will wrap and abbreviate all links shared on the site in the same way other URL-shortening services, such as Bitly, do.

Twitter said user security played a major role in implementing the new service.

"Since we show a shortened version of the original link, people will know which site the link points to," Twitter said in a statement. "This service also increases security. If users click links that are reported as malicious, we direct them to a page that warns them."

Twitter said that while it is putting the squeeze on links, it has no plans to squeeze out third-party link shorteners; those abbreviated links will continue to work on Twitter.

The link is shortened when the URL entered exceeds 13 characters, and a count appears under the box to let users know how close they are to exceeding their 140-character limit with shortened URL's character factored in.

Updated at 9 p.m. to correct that users know how many characters remain in new system.